Pipe Joint Failures often Result from Bad Glue Joints

Q. Is there a proper direction that the built-in coupling bell on the end of a pvc pipe should face?

A. Depends on who you ask, but my opinion is no, there is no “correct direction” to place the spigot and bell. Don’t worry about it, the procedure you use to glue the joint is much, much more important. For the record, those who have expressed a preference generally say the spigot (male end) should point downstream, ie; the bell end of the pipe should be on the end closest to the valve.

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If you think about it, a standard PVC coupling or tee will need to have spigots (male end) inserted into the sockets (female end) from both directions, with the flow and against the flow. So obviously it is not critical, or they would not make them with a socket on both ends! A bell end is just a socket molded into the pipe end, although the bell end does have a thinner wall than the socket end of most true couplings. And that can be a bit of a problem. There is less wall thickness in a bell to wear through. Add to that a poor job of gluing, or a bell that was not evenly stretched at the factory when it was made, and you have a weaker, thinner wall area that wears through faster. So leaks tend to occur at bell joints. Too much glue applied on the socket (female) end of the joint is a major problem, the glue beads up against the end of the spigot as it is shoved in, then the thick bead of glue just sits there inside the pipe, where it dries slower, and melts and weakens the pipe wall right where the end of the spigot is. The same problem can occur with standard fittings also, often in reverse since the typical fitting has a thicker wall than most pipe. That glue “bead” that so many people like to see form against the end of the fitting actually concentrates the glue, allowing it to dry slower and, as it does, it melts through the pipe wall at that point. This problem can be compounded if the pipe gets moved while the glue is still wet and the glue-softened pipe stretches.

Proper gluing is the key.

Use the correct glue. Different sizes and different types of pvc pipe and even different climates require different glues. Use the right glue for your pipe, pipe size, and climate. Read the instructions that came on the glue can. The glue dauber/applicator diameter should be 1/2 the pipe diameter. Smaller sizes will not apply glue quick enough and it will dry to much before you can get the spigot into the socket. Remember, pvc glue is more than just sticky, it actually melts the pipe slightly to “weld” the sections together.

1. apply pvc primer on both spigot and socket.

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2. apply glue on spigot (male)

3. apply glue in socket

4. apply glue on spigot (2nd coat)

5. insert and twist

6. hold 20-30 seconds

7. wipe off excess bead (not everyone recommends this but as noted, I think it is best.)

The second coat on the spigot end gets pushed to the outside of the joint if there is too much. So that is where you want to be generous with the glue. It’s easy to wipe off excess glue beaded on the outside of the pipe.

Want to know if the glue failed at a joint or turbulence was the problem? You can try some home-done forensics, “CSI for pipes”. Take the leaky joint/fitting that you cut out of the pipe and put it in a vise. Now cut the fitting lengthwise in half. If the glue joint was bad you will be able to use a flat blade screwdriver to break the spigot off from the socket in the sawed in half fitting, it will separate where it was glued. Often after you split and separate it you can see a channel where the water carved it’s way through the glue. You may also be able to see the thinner pipe wall area where the pipe stretched by holding it up to a bright light so that the light shines through the pipe wall.

Reference:Special thanks to the Lasco Company for reprinting an article by Larry Workman, applications engineer with the Lasco Company, that appeared in Grounds Maintenance Magazine, Apr 1987. One of the best articles I have ever seen on how to glue pvc pipe. The pipe gluing procedure I use, as described above, is derived from that article. To the best of my knowledge the Grounds Maintenance Magazine is no longer in business. Larry Workman is now a PVC Forensics Consultant and Trainer at: Expert4PVC Consulting, Mission Viejo, California.